French researchers reported an alarming finding this week at an HIV/AIDS conference in Baltimore--HIV, which targets and infects human immune system cells, also appears to be able to infect fat cells. Scientists from the Institut Cochin in Paris and at a research hospital in Suresnes, France, discovered by accident HIV DNA in the fat tissues of a patient taking part in a study on HIV-related lipodystrophy, which is marked by changes in fat distribution in the body. The researchers were studying fat cells taken from the patient's abnormal fatty abdominal deposits when they discovered that the cells were infected with HIV. A further analysis showed HIV in the fat cells of all seven study patients, all of whom were taking antiretroviral medications and had undetectable blood-based viral loads.

HIV infects immune system cells by first attaching to two receptors on the surface of the cells--called CCR5 and CXCR receptors--which serve as doorways that allow the virus to insert its genetic material into the cells. The researchers theorize that because fat cells also have CCR5 surface receptors, these cells are also vulnerable to HIV infection. It may also be possible that anti-HIV drugs somehow prime the virus to recognize the receptors on the fat cells that it normally wouldn't target, the researchers said. But they added that the precise mechanism of infection and the role of HIV antiretroviral drugs in the process is not yet known.

If it shown that all fat cells in all HIV patients are prone to infection, the implications could be staggering, said researcher Jacques Leibowich. "A person has about a kilogram [two pounds] of lymphocytes [immune system cells]," he said. "But someone like me has 15 kilograms [30 pounds] of fat. So fat cells could be the more important source " of viral reservoirs. Studies are now being launched to look for infected fat cells in other HIV patients, especially those who have not developed lipodystrophy and those who are not being treated with anti-HIV medications, Leibowich said.

The researchers say their findings could help explain how HIV manages to remain in latent reservoirs in the bodies of people who've cleared the infection from their blood and may help to shed light on why some HIV-positive people lose fat in some parts of their bodies and gain it in others. They also hope their discovery will enable the development of treatments that target HIV inside infected fat cells.